import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicReference;

/**
 * @author Dennis Li
 * @date 2020/9/27 19:02
 */
public class Animal {
    public void sleep(int a) {
        System.out.println("Animal sleep");
    }

    private static int a = 0;

    static {
        a = 1;
    }

    static public  void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        new ConcurrentHashMap<>();
        list.add(1);
        list.add(2);
        list.add(3);

        Iterator<Integer> iterator = list.iterator();

        iterator.remove();

        System.out.println(list.toString());

    }

    static class Mouse extends Animal {
        public void sleep() {
            AtomicReference<Object> reference = new AtomicReference<>();
            System.out.println("Mouse");
        }
    }

}
